The Sexual Offences Act 2003 (c. 42) is an act of the Parliament (for England and Wales).

It partly replaced the Sexual Offences Act 1956 (4 & 5 Eliz. 2. c. 69) with more specific and explicit wording. It also created several new offences such as non-consensual voyeurism, assault by penetration, causing a child to watch a sexual act, and penetration of any part of a corpse. It defines and sets legal guidelines for rape in English law. It is also the main legislation dealing with child sexual abuse.

The corresponding legislation in Scotland is the Sexual Offences (Scotland) Act 2009 and in Northern Ireland the Sexual Offences (Northern Ireland) Order 2008.

Part I of the act makes many changes to the sexual crimes laws in England and Wales (and to some extent Northern Ireland), almost completely replacing the Sexual Offences Act 1956 (4 & 5 Eliz. 2. c. 69).

Rape has been redefined from the Sexual Offences Act 1956 (4 & 5 Eliz. 2. c. 69), amended by the Sexual Offences (Amendment) Act 1976 and the Criminal Justice and Public Order Act 1994, to read:

A person (A) commits an offence if—

Rape previously did not include penetration of the mouth. The act also changes the way in which lack of consent may be proved, and section 75 and 76 of the act list circumstances in which lack of consent may be presumed.

Section 2 creates the offence of Assault by penetration. This offence is set out separately because rape is defined as requiring penile penetration. Therefore, non-consensual sexual penetration of the vagina or anus with either another part of the body (such as the fingers), or an object, must be prosecuted under this section. Section 2 closely mirrors section 1's definition of rape, including the same maximum sentence (life imprisonment), but does not include penetration of the mouth, and carries the additional requirement that "the penetration is sexual", i.e. performed for the purpose of either the offender's sexual gratification or the victim's sexual humiliation.